The Effects And Underlying Mechanisms Of HDAC2on Cognitive Improvement In An APP/PS1Mouse Model Of Alzheimer’s Disease

Background Alzheimer’s disease (AD) is one of progressive neurodegenerative diseases. The pathological features are insoluble P-amyloid (AP) plaques, neurofibrillary tangles (NFTs), neuron and synapse loss. Despite enormous research efforts, the etiology of AD remains obscure and puzzling. Genetic variants in the amyloid-precursor protein (APP) gene, presenilin (PS) gene and the Apolipoprotein (Apo) E4genotype have repeatedly been connected with AD. Environmental factors such as a Mediterranean diet, physical exercise, and exposure to toxins have been associated with AD. Epigenetic mechanisms, especially the abnormal acetylation of histone, are involved in the altered synaptic function and memory associated with Alzheimer’s disease (AD). Histone acetylation and deacetylation are catalytic by histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. Histone deacetylase2(HDAC2) has crucial roles in development and physiology in nervous system. HDAC2is mainly expressed in regions of the hippocampus including the area of CA1, CA3and DG, which shows that it has important functions in learning and memory formation. HDAC2negatively regulates learning and memory by modulating synaptic plasticity and long-lasting changes of neural circuits. HDAC2levels were significantly elevated in hippocampal area CA1and the entorhina cortex in Alzheimer’s disease compared with the same aged. Based on the functions of HDAC2mentioned above, we were interested in whether HDAC2knockout would facilitate AD pathogenesis.Methods The APP/PS1/HDAC2KO mice were produced by cross-breeding APP/PS1mice with HDAC2brain-specific knockout mice. To explore the effect of the deletion of HDAC2in APP/PS1mice, we examined the body length, body weight, brain weight and brain/body weight. The expression of HDAC2in the brain of4-old-month WT, AD, HDAC2KO and AD-HDAC2K0mice were analyzed by immunohistochemistry staining, immunofluorescence staining and Western blotting. The locomotor activity changes were examined by open field test and cognitive abilities were detected using novel object recognition test and Morris water maze in WT, AD, HDAC2KO and AD-HDAC2KO mice. Neuropathological amyloid depositions were quantified using immunohistochemistry and thioflavine-S staining. The soluble Aβ40and Aβ42peptide were determined by ELISA. The expression of brain BACE1, PS1, ADAM10, ADAM17, sAPPa, sAPPα, β-CTF and a-CTF were detected by Western blotting. The expression of plasticity association proteins were detected by Western blotting. The accumulation of P-AKT, P-GSK3β and P-CREB were detected by Western blotting.Results The body length, body weight of4-month-old AD-HDAC2K0mice were smaller and decreased compared with AD mice and WT mice. There were no significant differences in the brain weight and brain/body weight of each group. HDAC2staining showed an efficient deletion of HDAC2in the cerebral cortex and the hippocampal area. In addition, immunofluorescence staining also showed HDAC2expression in the hippocampal CA1and dentate gyrus (DG) of WT and AD mice, but not in HDAC2K0or AD-HDAC2K0mice, in consistent with the Western blotting results. The deletion of HDAC2improved cognitive deficits as indicated by attenuation of the abnormal autonomous behaviors, by amelioration of the learning and memory with increasing in the novel object recognition, with increasing in the target-quadrant abidance and the crossing-target number in Morris water maze in AD mice. Compared with AD mice, the AD-HDAC2K0mice exhibited fewer numbers and less plaque area in the hippocampus and cortex using Thioavine-S and immunohistochemistry staining. In addition, the soluble A040and Aβ42peptide of AD-HDAC2K0mice were significantly decreased compared with AD mice. The deletion of HDAC2in AD mice could up-regulate the expression of sAPPa, and decreased the expression of BACE1, PS1and sAPPβ. The expression of ADAM10and ADAM17showed no differences. The increased P-AKT and P-GSK3β were also detected in the brain of AD-HDAC2KO mice by Western blotting.Conclusions The present study shows that the knockout of HDAC2mitigates Alzheimer’s disease pathogenesis in an APP/PS1transgenic mouse model. The AD-HDAC2K0mice showed improved spatial memory and cognitive function, partly through reducing amyloid plaque formation, up-regulating plasticity associated proteins and inhibiting GSK3β activity compared with AD mice. Our studies suggest that HDAC2may play a role in the development of AD-like neuropathology. Background Insulin plays diverse roles, including learning and memory, in the central nervous system. Insulin receptors are dispersed throughout the brain, with the highest density located in the cerebral cortex and hippocampus where insulin signaling contributes to neuronal survival, synaptogenesis and asynaptic remodeling, dendritic spine formation and excitatory synapse development in hippocampal neurons. Sirtuins, or Sir2family proteins, are NAD+-dependent class III histone deacetylases. SIRT1has also been suggested to be involved in the processes of energy homeostasis, synaptic plasticity and memory formation in the brain. However, whether insulin is directly involved in regulating SIRT1expression in neurons or whether it affects synapses remains largely unknown.Methods We attempt to find the optimum density of insulin drug using MTT assay method. LY294002, a phosphatidylinositol3-kinase inhibitor, was used to test whether insulin regulates the level of SIRT1through PDK/Akt signal pathway. Western blotting was used to detect the expression of SIRT1protein in SH-SY5Y cells by insulin regulation. In addition, the SIRT1inhibitor and SIRT1-siRNA were used to examine how insulin induces neurite outgrowth in SH-SY5Y cells.Results Here, we show that insulin promotes neurite outgrowth and increases SIRT1expression in SH-SY5Y cells. Western blotting analysis find the time-dependent regulation of insulin on the expression of SIRT1. LY294002, a phosphatidylinositol3-kinase inhibitor, inhibited the expression of insulin-induced increases in SIRT1. Conversely, the downregulation of SIRT1using a SIRT1inhibitor and SIRT1-siRNA resulted in a significant reduction in the length of neurite outgrowth.Conclusion Taken together, these results suggest that the regulation of SIRT1by insulin is important for the neurite outgrowth of neuroblastoma cells.